What is the function of the tumor necrosis factor superfamily Pathway?

The tumor necrosis factor superfamily pathway regulates normal functions such as immune responses, hematopoiesis, and morphogenesis and induces cellular proliferation, survival, differentiation, or apoptosis. The superfamily which consists of 19 proteins and 29 receptors has also been implicated in tumorigenesis, transplant rejection, septic shock, viral replication, bone resorption, rheumatoid arthritis, and diabetes.

What proteins are included in the TNF superfamily?

The 19 ligands mediate their cellular response through receptors that belong to the TNF receptor (TNFR) superfamily, and they are characterized by the presence of a cysteine-rich domain (CRD) in the extracellular portion (1-2). Based upon their cytoplasmic sequences and signaling properties, these TNF receptors can be classified into three major groups (1).

TNF Receptors containing the Death Domain

The first group all contain a DD (Death Domain) in the cytoplasmic tail. These molecules cause activation of the caspase cascade and induction of apoptosis (3).

Included in this first group are Fas/CD95/Apo1/APT1, TNFR1/CD120a/p55-R/TNFAR/TNFR60, DR3/TRAMP/WSL1/LARD/WSLLR/DDR3/TR3/Apo3, DR4/TRAILR1/Apo2, DR5/TRAILR2/KILLER/TRICK2A/TRICKB, and DR6/TR7. Fas, DR4, and DR5 interact with the FADD (Fas-Associated Death Domain) while TNFR1 and DR3 interact with the adaptor TRADD (TNFR-Associated Death Domain).

TNF Receptors containing TRAF Interacting Motifs (TIM)

The second group of TNF receptors includes receptors that contain one or more TIM (TRAF Interacting Motifs) in their cytoplasmic tails. Activation of TIM-containing TNF receptors leads to recruitment of TRAF family members and activation of multiple signal transduction pathways, such as NF-KappaB (Nuclear Factor-KappaB), JNK (Jun N-terminal Kinase), p38, ERK (Extracellular Signal Regulated Kinase), and PI3K (Phosphoinisitide-3 Kinase) (4).

Included in this second group are: TNFR2/p75/CD120b/TNFR80/TNFBR, CD40/p50/Bp50, CD30/Ki-1/D1S166E, CD27/Tp55/S152, TNFR2-RP/TNFCR/TNFRIII, LT-BetaR, OX40/ CD134/ACT35/TXGP1L, 4-1BB/CD137/ILA, BAFFR, BCMA/BCM, TACI/CAML interactor, RANK/TRANCE-R, p75NGFR, HVEM (Herpes Virus Entry Mediator)/HveA/ATAR/TR2/ LIGHTR, GITR/AITR/ TNFRSF18, TROY/TAJ, EDAR, XEDAR/EDA-A2R, RELT, and Fn14.

TRAFs are a major group of intracellular adaptors that bind directly or indirectly to many members of the TNF receptor superfamily. Six mammalian TRAFs, TRAF1 through TRAF6, have been identified. TRAFs can induce the activation of several kinase cascades that ultimately lead to the activation of signal transduction pathways such as NF-KappaB, JNK, ERK, p38, and PI3K, which can regulate cellular processes ranging from cell proliferation and differentiation to apoptosis.

TNF Receptors that are Decoy Receptors

The third group of TNF receptor family members does not contain functional intracellular signaling domains or motifs. Although this group of receptors cannot provide intracellular signaling, they can effectively compete with the other two signaling groups of receptors for their corresponding ligands. These DcR (Decoy Receptors) therefore function by impeding the activation of signal transduction pathways by other TNF receptors (5).

Included in this third TNF receptor group are: DcR1/TRID/TRAIL-R3, DcR2/ TRUNDD/TRAIL-R4, DcR3, and Opg.

TNF receptor regulation

The TNFR superfamily contains a large number of proteins that regulate a very broad array of developmental and differentiating processes. Indeed, a number of biologic TNF blocking therapies are being used now to inhibit the inflammation associated with Crohn’s disease and rheumatoid arthritis. The continued examination of TNFR signal transduction will provide the tools for receptor or tissue specific interventions, allowing more targeted treatments that have fewer side effects (6).

Tumor necrosis factor superfamily pathway

TNF Superfamily Pathway
Cartoon schematic showing what symbols used in the pathway schematic represent.
TNF Superfamily Pathway
Cartoon schematic showing what symbols used in the pathway schematic represent.


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